1. Field of the Invention
The corn rootworm (CRW) is a major threat to the production of corn in North America. Costs associated with attempts to control the pest combined with monetary losses due to crop damage can exceed $1 billion per year. Moreover, the CRW causes an additional $100 million in damage and control costs on cucurbits, peanuts and soybeans; adult insects have caused considerable damage to many fruits and have been implicated as carriers of some plant diseases as well.
Chemical pesticides for the control of the CRW pest complex are applied to 12-16 million hectares per year. These chemicals often have been applied as a preventive measure, sometimes unnecessarily, thus increasing the health risks imposed on the general population as well as on livestock and other farm and domestic animals and wildlife.
The need for an effective agent for the control of CRW which is also environmentally safe is thus well-established. This invention relates to a toxicant-bait formulation effective for controlling corn rootworm and to its method of use.
2. Description of the Relevant Art
An interesting relationship between insect herbivores and their host plants is the phenomenon exhibited by insects feeding compulsively on phytochemicals that are toxic to other insects. This phenomenon occurs between CRW and their ancestral plant hosts, the Curbitaceae. These plants produce very bitter compounds, cucurbitacins, which are phagostimulants for many of the CRW pest species (Metcalf, R. L. 1986. J. Chem. Ecol. vol. 12, pp. 1109-1124; Metcalf and Lampman. 1989. J. Econ. Entomol. vol. 82, pp. 1620-1625; Tallamy and Kriachik. 1989. Amer. Nat. vol. 133, pp. 766-786; Metcalf and Rhodes. 1990. In: Biology and utilization of the cucurbitaceae. Bates et al., eds. Comstock, Ithaca, N.Y.). No evidence of acute toxicity exhibited by the compounds has been produced (Tallamy and Halaweish. 1993. Environ. Entomol. vol. 22, pp. 925-932).
There has been a major effort to replace ineffective and environmentally undesirable soil insecticides with baits laced with cucurbitacins and toxins (Metcalf et al. 1987. J. Econ. Entomol. vol. 80, pp. 870-875; Lance, D. R. 1988. J. Econ. Entomol. vol. 81, pp. 1359-1362; Weissling et al. 1989. Entomol. Exp. Appl. vol. 53, pp. 219-228; Lance and Sutter. 1990. J. Econ. Entomol. vol. 83, pp. 1085-1090; Lance and Sutter. 1991. J. Econ. Entomol. vol. 84, pp. 1861-1868; Weissling and Meinke. 1991. Environ. Entomol. vol. 20, pp. 945-952; Brust and Foster. 1995. J. Econ. Entomol. vol. 88, pp. 112-116). Lacing the baits with cucurbitacins causes the beetles to compulsively feed on them, and they die from the insecticides present in the composition. The increased feeding brought on by the presence of the cucurbitacins has resulted in a reduction in the amount of insecticide necessary for an effective formulation by 90-95%. These baits are pest specific and are capable of killing 99% of the beetles consuming them (Tallamy and Halaweish, supra). Carbaryl, a semiochemical-based insecticide bait specific to CRW, for example, has been developed by a research team comprised of entomologists from USDA, ARS, universities, and industry (Chandler et al. 1995. In: Clean water, clean environment. 21st centure team agriculture, working to protect water resources. Conf. Proceed. vol. 1, pp. 29-32) and is currently under commercial development. The baits are currently being evaluated in areawide Integrated Pest Management (IPM) programs for CRW control on limited corn acreage in the Corn Belt (Chandler et al., supra).
The goal of agronomists in refining IPM practices is to rely less on synthetic chemicals in baits and, if possible, to find other approaches to managing the CRW (Butler, R. E. 1992. Seed World. vol. 130, pp. 8-10). Various attempts have therefore been made to develop formulations effective for controlling corn rootworm. The baits laced with insecticides and feeding stimulants, e.g. those reported by Metcalf et al., supra, are prepared from Cucurbita fruits which were dried, ground and impregnated with insecticides and volatile attractants. These baits were then scattered over plots of sweet corn, with some of the bait on the leaves and silks of the ears of corn. Lance and Sutter (1992. J. Econ. Entomol. vol. 85, pp. 967-973) also described a bait formulation containing an insecticide, a feeding stimulant and volatile attractants. In both instances, volatile attractants were included since cucurbitacins, although recognized as powerful feeding stimulants, are not effective as attractants. Delivery of the insecticide was therefore accomplished by first attracting the insect, then stimulating it to feed on the insecticide-laced bait.
Other compositions and methods have also been utilized in attempts to control the corn rootworm. Guss et al. (U.S. Pat. No. 4,565,695, 1986) suggest the use of synthetic pheromone for mating disruption or for use in combination with larval insecticides. Doane et al. (U.S. Pat. No. 5,464,618, 1995) describe a gustatory stimulant comprising dried and powdered plant material containing cucurbitacins, a lubricant and an adherent to be used in combination with an insecticide for adult beetles. Munson et al. (U.S. Pat. No. 5,571,522, 1996) describe a feeding stimulant to be used in combination with an insecticide where the feeding stimulant is corn germ.
All these various approaches have suffered from a lack of consistency in the delivery of the insecticide to the targeted insect. While cucurbitacins are potent feeding stimulants, they do not serve as attractants at all, so the targeted pests must be in the immediate vicinity of the compounds in order for them to be effective. Dry formulations have thus resulted in a substantial portion of the insecticide being wasted because it is never consumed. This waste is deleterious not only because of cost and ineffectiveness, but also because it results in insecticide remaining in the fields to contaminate the soil, ground water and other sources of water such as lakes, rivers and streams.